Mounting mat including inorganic nanoparticles and method for making the same

ABSTRACT

The present invention relates to a mounting mat for mounting a pollution control device in a catalytic converter, the mounting mat comprising a non-woven mat of inorganic fibers having distributed therein inorganic particles having an average diameter of 1 nm to 100 nm and wherein the mounting mat is free of organic binder or contains organic binder in an amount of not more than 5% by weight, based on the total weight of the mounting mat. The invention further relates to a pollution control device including the mounting mat and to a method of making the mounting mat.

FIELD OF THE INVENTION

The present invention relates to a mounting mat suitable for mounting apollution control element in a pollution control device. In particularthe present invention relates to a mounting mat that includes a powderof inorganic nanoparticles. The invention further relates to a method ofmaking such a mounting mat. Still further the present invention relatesto a pollution control device including the mounting mat.

BACKGROUND

Pollution control devices are employed on motor vehicles to controlatmospheric pollution. Such devices include a pollution control element.Exemplary pollution control devices include catalytic converters anddiesel particulate filters or traps. Catalytic converters typicallycontain a ceramic monolithic structure having walls that support thecatalyst. The catalyst typically oxidizes carbon monoxide andhydrocarbons, and reduces the oxides of nitrogen in engine exhaust gasesto control atmospheric pollution. The monolithic structure may also bemade of metal. Diesel particulate filters or traps typically includewall flow filters that are often honeycombed monolithic structures made,for example, from porous ceramic materials. The filters typically removesoot and other exhaust particulate from the engine exhaust gases. Eachof these devices has a housing (typically made of a metal like stainlesssteel) that holds the pollution control element. Monolithic pollutioncontrol elements, are often described by their wall thickness and thenumber of openings or cells per square inch (cpsi). In the early 1970s,ceramic monolithic pollution control elements with a wall thickness of12 mil (304 micrometer) and a cell density of 300 cpsi (47 cells percm²) were common (“300/12 monoliths”).

As emission laws become more stringent, wall thicknesses have decreasedas a way of increasing geometric surface area, decreasing heat capacityand decreasing pressure drop of the monolith. The standard hasprogressed to 900/2 monoliths. With their thin walls, ceramic monolithicstructures are fragile and susceptible to vibration or shock damage andbreakage. The damaging forces may come from rough handling or droppingduring the assembly of the pollution control device, from enginevibration or from travel over rough roads. The ceramic monoliths arealso subject to damage due to high thermal shock, such as from contactwith road spray.

The ceramic monoliths have a coefficient of thermal expansion generallyan order of magnitude less than the metal housing which contains them.For instance, the gap between the peripheral wall of the metal housingand the monolith may start at about 4 mm, and may increase a total ofabout 0.33 mm as the engine heats the catalytic converter monolithicelement from 25° C. to a maximum operating temperature of about 900° C.At the same time, the metallic housing increases from a temperature ofabout 25° C. to about 530° C. Even though the metallic housing undergoesa smaller temperature change, the higher coefficient of thermalexpansion of the metallic housing causes the housing to expand to alarger peripheral size faster than the expansion of the monolithicelement. Such thermal cycling typically occurs hundreds or thousands oftimes during the life of the vehicle.

To avoid damage to the ceramic monoliths from road shock and vibrations,to compensate for the thermal expansion difference, and to preventexhaust gases from passing between the monoliths and the metal housings(thereby bypassing the catalyst), mounting mats are disposed between theceramic monoliths and the metal housings. The process of placing themonolith within the housing is also called canning and includes suchsteps as wrapping a sheet of mat material around the monolith, insertingthe wrapped monolith into the housing, pressing the housing closed, andwelding flanges along the lateral edges of the housing.

Typically, the mounting mat materials include inorganic fibers,optionally intumescent materials, organic binders, fillers and otheradjuvants. Known mat materials, used for mounting a monolith in ahousing are described in, for example, U.S. Pat. No. 3,916,057 (Hatch etal.), U.S. Pat. No. 4,305,992 (Langer et al.), U.S. Pat. No. 4,385,135(Langer et al.), U.S. Pat. No. 5,254,410 (Langer et al.), U.S. Pat. No.5,242,871 (Hashimoto et al.), U.S. Pat. No. 3,001,571 (Hatch), U.S. Pat.No. 5,385,873 (MacNeil), and U.S. Pat. No. 5,207,989 (MacNeil), GB1,522,646 (Wood), published Aug. 23, 1978, Japanese Kokai No.: J.P. Sho.58-13683, published Jan. 26, 1983 (i.e., Pat Appln Publn No. J.P. Hei.2-43786 and Appln No. J.P. Sho. 56-1 12413), and Japanese Kokai No.:J.P. Sho. 56-85012, published Jul. 10, 1981 (i.e., Pat. Appln No. Sho.54-168541). Mounting materials should remain very resilient at a fullrange of operating temperatures over a prolonged period of use.

A need exists for a mounting system which is sufficiently resilient andcompressible to accommodate the changing gap between the monolith andthe metal housing over a wide range of operating temperatures and alarge number of thermal cycles. While the state of the art mountingmaterials have their own utilities and advantages, there remains anongoing need to improve mounting materials for use in pollution controldevices. Additionally, one of the primary concerns in forming themounting mat is balancing between the cost of the materials andperformance attributes. It is desirable to provide such a high qualitymounting system at the lowest possible cost.

A particular need exists to provide a mounting mat or system thatprovides an improved holding pressure at ambient temperature as well asat the operating temperatures to which the pollution control device thatincludes the mounting mat may be exposed to. It is furthermoreparticularly desired to find a way to improve the holding pressure inintumescent as well as in non-intumescent mounting mats. Furthermore, itwould be desired to find a solution that can be used even when themounting mat is free of organic binder or low in organic binder content.To find such a solution is particularly desirable as the use of largeamounts of organic binder in a mounting mat is undesirable as it maylower the performance of the mounting mat and/or is environmentallydisadvantageous as the binder usually needs to be burnt out during firstuse of the pollution control device. Developing mounting mats that arelow in binder content and that have an improved holding pressure hasproven to be particularly challenging for intumescent mounting matsbecause these mats are prone to cracking during the mounting of the matin the pollution control device.

US 2006/008395 (Ten Eyck et al.) discloses a surface treatment ofinorganic fibers and in particular of leached glass fibers to achieve anincreased holding performance of non-intumescent mats. However, themethod of manufacturing disclosed to obtain the coated fibers iscumbersome and expensive as it involves the use of a slurry of colloidalmaterial for treating the fibers. The treatment of the fibers furtherincludes a heat treatment which means an increased energy cost in themanufacturing.

Accordingly, it would be a further desire to find a method of makingmounting mats of improved performance and that can be manufactured in aneasy and convenient way at a lower cost.

SUMMARY

In a first aspect, the invention provides a mounting mat for mounting apollution control device in a catalytic converter, the mounting matcomprising a non-woven mat of inorganic fibers having distributedtherein inorganic particles having an average diameter of 1 nanometer(nm) to 100 nm and wherein the mounting mat is free of organic binder orcontains organic binder in an amount of not more than 5% by weight,based on the total weight of the mounting mat.

In a second aspect, the invention provides a pollution control devicehaving a housing, a pollution control element disposed within thehousing, and a mounting mat disposed between the pollution controlelement and the housing for positioning the pollution control elementand for absorbing mechanical and thermal shock, wherein the mounting matcomprises a mounting mat as described above.

In a third aspect, the invention provides a method of making a mountingmat as defined above comprising the steps of:

-   -   (i) supplying inorganic fibers through an inlet of a forming box        having an open bottom positioned over a forming wire to form a        mat of fibers on the forming wire, the forming box having a        plurality of fiber separating rollers provided in at least one        row in the housing between the inlet and housing bottom for        breaking apart clumps of fibers and an endless belt screen;    -   (ii) capturing clumps of fibers on a lower run of the endless        belt beneath fiber separating rollers and above the forming        wire;    -   (iii) conveying captured clumps of fibers on the endless belt        above fiber separating rollers to enable captured clumps to        release from the belt and to contact and be broken apart by the        rollers;    -   (iv) transporting the mat of fibers out of the forming box by        the forming wire; and    -   (v) compressing the mat of fibers and restraining the mat of        fibers in its compressed state thereby obtaining a mounting mat        having a desired thickness suitable for mounting a pollution        control element in the housing of a catalytic converter;        and wherein inorganic particles having an average diameter of 1        nm to 100 nm are provided in the mounting mat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic perspective view of a forming box;

FIG. 2 shows a schematic side view of a forming box;

FIG. 3 shows a detailed view of the forming box shown in FIG. 2; and

FIG. 4 shows a schematic view of a pollution control device.

The mounting mats in accordance with the present invention can beproduced in a cost effective and easy way and generally have an improvedperformance, e.g. holding performance at ambient conditions as well asunder operating conditions, when used to mount a pollution controlelement into a pollution control device. Furthermore, the use of theinorganic nanoparticles (particles having an average diameter of 1 nm to100 nm) in a particular embodiment offers the possibility to obtainmounting mats that are low (not more than 5% by weight of organicbinder, for example, not more than 3% by weight of organic binder or notmore than 2% by weight of organic binder) in organic binder content orthat are free of organic binder. In particular, intumescent mountingmats of improved performance and low in organic binder content or freeof organic binder can be obtained.

The mounting mat includes inorganic nanoparticles. The inorganicnanoparticles have an average diameter between 1 nm and 100 nm, forexample between 2 nm and 80 nm, for example between 3 nm and 60 nm orbetween 3 nm and 50 nm. In a particular embodiment, the average diameteris between 8 nm and 45 nm. The inorganic nanoparticles can have anyshape although generally, the particles will be generally spherical inshape or will have a disc like shape. To the extent that the particlesare not spherical, the term ‘diameter’ should be understood to mean themeasure of the largest dimension of the particle. Also, in theconnection with the present invention, the average diameter is typicallythe weight average diameter.

The inorganic nanoparticles may vary widely in their chemicalcomposition although they typically comprise oxides such as oxides ofsilica, alumina, titanium and/or zirconia. Further inorganicnanoparticles include silicates containing Mg, Ca, Al, Zr, Fe, Na, Kand/or Li such as micas, clays and zeolites. Commercially availablenanoparticles that can be used include those available under the tradedesignation “NALCO”, from Nalco Chemical Inc, Leiden, Netherlands,“AEROSIL”, from Evonik Industries, Frankfurt, Germany, “LAPONITE” fromRockwood Additives Ltd, Widnes, UK, “MICROLITE”, from Elkem ASA,Voogsbygd, Norway, “BENTONITE” from Bentonite Performance Minerals LLC,Houston, Tex., USA, and “BINDZIL” from Eka Chemicals AB, Gothenburg,Sweden.

The inorganic nanoparticles are typically included in the mounting matin an amount of at least 0.5% by weight based on total weight of themat. An exemplary range is from 0.5 to 10%, for example, from 0.6% byweight to 8% by weight or from 0.8% by weight to 7% by weight.

The inorganic nanoparticles may be provided in the mounting mat in avariety of ways. For example, in one embodiment, the inorganicnanoparticles may be sprayed on the fibers from a solution or dispersion(e.g., an aqueous dispersion) before the fibers are being laid into anon-woven web and formed into a mounting mat. According to anotherembodiment, a dispersion of nanoparticles may be used to impregnate aformed non-woven web or mounting mat or the dispersion may be sprayedthereon. In yet a further embodiment the nanoparticles may be added as adry powder together with the fibers in a dry air laying process, inparticular the dry air layer process described further below, forexample using a forming machine as illustrated in FIGS. 1-3.

Fibers used in the mounting mat are generally those fibers that arecapable of withstanding the temperatures of the exhaust gas to whichthey may be exposed. Typically, the fibers used are inorganic fibersinclude refractory ceramic fibers, glass fibers, and polycrystallineinorganic fibers. Examples of inorganic fibers materials includealumina, silica, alumina-silica such as mullite, glass, ceramic, carbon,silicon carbide, boron, aluminoborosilicate, zirconia, titania, etc.These inorganic materials may be used singly, or at least two of themmay be mixed and used in combination. For example, the inorganic fibermaterial may comprise alumina alone, or another inorganic material mayfurther be used in combination with alumina, such as silica.Alumina-silica fiber materials may contain further metal oxides such assodium, potassium, calcium, magnesium, and boron oxides. The inorganicfibers may be used either individually or in combination of two or morekinds. Among these inorganic fibers, ceramic fibers such as aluminafibers, silica fibers and alumina-silica fibers may be used in oneparticular embodiment, alumina fibers and alumina-silica fibers may beused in another embodiment, and polycrystalline alumina-silica fibersmay be used in yet a further embodiment.

In a particular embodiment, the inorganic fibers of the mat compriseceramic fibers that are obtained from a sol-gel process. By the term“sol-gel” process is meant that the fibers are formed by spinning orextruding a solution or dispersion or a generally viscous concentrate ofthe constituting components of the fibers or precursors thereof. Thesol-gel process is thus to be contrasted with a process of melt formingfibers whereby the fibers are formed by extruding a melt of thecomponents of the fibers. A suitable sol-gel process is for exampledisclosed in U.S. Pat. No. 3,760,049 (Borer et al.), wherein there istaught to form the ceramic fibers by extruding a solution or dispersionof metal compounds through orifices thereby forming continuous greenfibers which are then fired to obtain the ceramic fibers. The metalcompounds are typically metal compounds that are calcinable to metaloxides. Often the sol-gel formed fibers are crystalline orsemicrystalline, which are known in the art as polycrystalline fibers.Examples of solutions or dispersions of metal compounds to form fibersaccording to a sol-gel process include aqueous solutions of anoxygen-containing zirconium compound, such as zirconium diacetate,containing colloidal silica, such as disclosed in U.S. Pat. No.3,709,706 (Sowman). A further example includes an aqueous solution ofwater-soluble or dispersible aluminum and boron compounds, such asaqueous basic aluminum acetate, or a two-phase system comprising anaqueous mixture of a colloidal dispersion of silica and water-soluble ordispersible aluminum and boron compounds. Other representativerefractory metal oxide fibers which can be made in a sol-gel processinclude zirconia, zircon, zirconia-calcia, alumina, magnesium aluminate,aluminum silicate, and the like. Such fibers additionally can containvarious metal oxides, such as iron oxide, chromia, and cobalt oxide.

Ceramic fibers which are useful in the mounting mat includepolycrystalline oxide ceramic fibers such as mullites, alumina, highalumina aluminosilicates, aluminosilicates, zirconia, titania, chromiumoxide and the like. Preferred fibers, which are typically high alumina,crystalline fibers, comprise aluminum oxide in the range from about 60to about 98 percent by weight and silicon oxide in the range from about40 to about 2 percent by weight. These fibers are commerciallyavailable, for example, under the trade designations “NEXTEL 550” fromthe 3M Company, St. Paul, Minn., “SAFFIL” available from Dyson GroupPLC, Sheffield, UK, “MAFTEC” available from Mitsubishi Chemical Corp.,Tokyo, Japan, “FIBERMAX” from Unifrax, Niagara Falls, N.Y., and “ALTRA”from Rath GmbH, Germany.

Suitable polycrystalline oxide ceramic fibers further includealuminoborosilicate fibers preferably comprising aluminum oxide in therange from about 55 to about 75 percent by weight, silicon oxide in therange from less than about 45 to greater than zero (preferably, lessthan 44 to greater than zero) percent by weight, and boron oxide in therange from less than 25 to greater than zero (preferably, about 1 toabout 5) percent by weight (calculated on a theoretical oxide basis asAl₂O₃, SiO₂, and B₂O₃, respectively).

The aluminoborosilicate fibers preferably are at least 50 percent byweight crystalline, more preferably, at least 75 percent, and mostpreferably, about 100% (i.e., crystalline fibers). Aluminoborosilicatefibers are commercially available, for example, under the tradedesignations “NEXTEL 312” and “NEXTEL 440” from the 3M Company.

The ceramic fibers obtainable through a sol-gel process are typicallyshot free or contain a very low amount of shot, typically less than 1%by weight based on total weight of the ceramic fibers. Also, the ceramicfibers will typically have an average diameter between 1 micrometer and16 micrometers. In a preferred embodiment, the ceramic fibers have anaverage diameter of 5 micrometers or more and preferably the ceramicfibers are free or essentially free of fibers having a diameter of lessthan 3 micrometers, more preferably the ceramic fiber layer will be freeor essentially free of fibers that have a diameter of less than 4micrometers. Essentially free here means that the amount of such smalldiameter fibers is not more than 1% by weight, preferably not more than0.1% by weight of the total weight of fibers in the ceramic fiber layer.

In a further embodiment, the inorganic fibers used may comprise heattreated ceramic fibers sometimes called annealed ceramic fibers.Annealed ceramic fibers may be obtained as disclosed in U.S. Pat. No.5,250,269 (Langer) or WO 99/46028, published Sep. 16, 1999. According tothe teaching of these documents, annealed ceramic fibers may be obtainedby annealing melt-formed refractory ceramic fibers at a temperature ofat least 700° C. By annealing the ceramic fibers, fibers are obtainedthat have an increased resilience. Typically, a resilience value of atleast 10 kPa may be obtained under the test conditions set out in U.S.Pat. No. 5,250,269 (Langer). The melt-formed refractory ceramic fiberssuitable for annealing, can be melt-blown or melt-spun from a variety ofmetal oxides, preferably a mixture of Al₂O₃ and SiO₂ having from 30 to70% by weight of alumina and from 70 to 30% by weight of silica,preferably about equal parts by weight. The mixture can include otheroxides such as B₂O₃, P₂O₅, and ZrO₂. Suitable melt-formed refractoryceramic fibers are available from a number of commercial sources andinclude these known under the trade designation “FIBERFRAX” fromCarborundum Co., Niagara Falls, N.Y., “CERAFIBER” and “KAOWOOL” fromThermal Ceramics Co., Augusta, Ga.; “CER-WOOL” from Premier RefractoriesCo., Erwin, Tenn.; and “SNSC” from Shin-Nippon Steel Chemical, Tokyo,Japan. The manufacturer of ceramic fibers known under the tradedesignation “CER-WOOL” states that they are melt-spun from a mixture ofby weight 48% silica and 52% alumina and have an average fiber diameterof 3-4 micrometers. The manufacturer of ceramic fibers known under thetrade designation “CERAFIBER” states that they are meltspun from amixture of by weight 54% silica and 46% alumina and have an averagefiber diameter of 2.5-3.5 micrometers. The manufacturer of ceramicfibers “SNSC 1260-D 1” states that they are melt-formed from a mixtureof by weight 54% silica and 46% alumina and have an average fiberdiameter of about 2 micrometers.

In a particular embodiment, the fibers used include glass fibers and inparticular magnesium aluminium silicate glass fibers. Examples ofmagnesium aluminium silicate glass fibers that can be used include glassfibers having between 10 and 30% by weight of aluminium oxide, between52 and 70% by weight of silicon oxide and between 1 and 12% of magnesiumoxide. The weight percentage of the aforementioned oxides are based onthe theoretical amount of Al₂O₃, SiO₂ and MgO. It will further beunderstood that the magnesium aluminium silicate glass fiber may containadditional oxides. For example, additional oxides that may be presentinclude sodium or potassium oxides, boron oxide and calcium oxide.Particular examples of magnesium aluminium silicate glass fibers includeE-glass fibers which typically have a composition of about 55% of SiO₂,15% of Al₂O₃, 7% of B₂O₃, 19% of CaO, 3% of MgO and 1% of other oxides;S and S-2 glass fibers which typically have a composition of about 65%of SiO₂, 25% of Al₂O₃ and 10% of MgO and R-glass fibers which typicallyhave a composition of 60% of SiO₂, 25% of Al₂O₃, 9% of CaO and 6% ofMgO. E-glass, S-glass and S-2 glass are available, for example, fromAdvanced Glassfiber Yarns LLC and R-glass is available from Saint-GobainVetrotex. The glass fibers are typically chopped magnesium aluminiumsilicate glass fibers and typically free of or essentially free of shot,i.e. having not more than 5% by weight of shot.

In a particular embodiment, heat treated glass fibers may be used. Ithas been found that heat treating glass fibers may improve the heatresistance of the glass fibers. Glass fibers may be heat treated at atemperature of up to about 50° C. or 100° C. below the softening ormelting point of the glass. Generally, the minimum temperature for heattreatment of the glass will be about 400° C. although lower temperaturesof for example at least 300° C. are conceivable as well. Nevertheless, alower temperature will typically require a longer exposure to heat inorder to achieve the desired increase in heat resistance of the glassfibers. With a temperature of between 300° C. and about 50° C. below thesoftening or melting point of the glass, the heat treatment willtypically take about 2 minutes to about 1 hour, for example, 5 minutesto 30 minutes.

In a particular embodiment in connection with the present invention, theinorganic fibers of the mounting mat may comprise biosoluble fibers. Asused herein, “biosoluble fibers” refers to fibers that are decomposablein a physiological medium or a simulated physiological medium.Physiological medium includes, but is not limited to, those bodilyfluids typically found in the respiratory tract such as, for example,the lungs of animals or humans. As used herein, “durable” refers tofibers that are not biosoluble.

Biosolubility can be estimated by observing the effects of directimplantation of the fibers in test animals or by examination of animalsor humans that have been exposed to fibers. Biosolubility can also beestimated by measuring the solubility of the fibers as a function oftime in simulated physiological medium such as saline solutions,buffered saline solutions, or the like. One such method of determiningsolubility is described in U.S. Pat. No. 5,874,375 (Zoitas et al.).Typically, biosoluble fibers are soluble or substantially soluble in aphysiological medium within about 1 year. As used herein, the term“substantially soluble” refers to fibers that are at least about 75weight percent dissolved. In some embodiments, at least about 50 percentof the fibers are soluble in a physiological medium within about sixmonths. In other embodiments, at least about 50 percent of the fibersare soluble in a physiological fluid within about three months. In stillother embodiments, at least about 50 percent of the biosoluble fibersare soluble in a physiological fluid within at least about 40 days. Forexample, the fibers can be certified by the Fraunhofer Institut aspassing the tests for the biopersistence of high temperature insulationfibers in rats after intratracheal instillation (i.e., the fibers have ahalftime less than 40 days).

Yet another approach to estimating the biosolubility of fibers is basedon the composition of the fibers. For example, Germany proposed aclassification based on a carcingenicity index (KI value). The KI valueis calculated by a summation of the weight percentages of alkaline andalkaline-earth oxides and subtraction of two times the weight percent ofaluminum oxide in inorganic oxide fibers. Inorganic fibers that arebiosoluble typically have a KI value of about 40 or greater.

Biosoluble inorganic fibers suitable for use in the present inventiontypically include, but are not limited to, inorganic oxides such as, forexample, Na₂O, K₂O, CaO, MgO, P₂O₅, Li₂O, BaO, or combinations thereofwith silica. Other metal oxides or other ceramic constituents can beincluded in the biosoluble inorganic fibers even though theseconstituents, by themselves, lack the desired solubility but are presentin low enough quantities such that the fibers, as a whole, are stilldecomposable in a physiological medium. Such metal oxides include, forexample, Al₂O₃, TiO₂, ZrO₂, B₂O₃, and iron oxides. The biosolubleinorganic fibers can also include metallic components in amounts suchthat the fibers are decomposable in a physiological medium or simulatedphysiological medium.

In one embodiment, the biosoluble inorganic fibers include oxides ofsilica, magnesium, and calcium. These types of fibers are typicallyreferred to as calcium magnesium silicate fibers. The calcium magnesiumsilicate fibers usually contain less than about 10 weight percentaluminum oxide. In some embodiments, the fibers include from about 45 toabout 90 weight percent SiO₂, up to about 45 weight percent CaO, up toabout 35 weight percent MgO, and less than about 10 weight percentAl₂O₃. For example, the fibers can contain about 55 to about 75 weightpercent SO₂, about 25 to about 45 weight 30 percent CaO, about 1 toabout 10 weight percent MgO, and less than about 5 weight percent Al₂O₃.

In a further embodiment, the biosoluble inorganic fibers include oxidesof silica and magnesia. These types of fibers are typically referred toas magnesium silicate fibers. The magnesium silicate fibers usuallycontain from about 60 to about 90 weight percent SiO₂, up to about 35weight percent MgO (typically, from about 15 to about 30 weight 5percent MgO), and less than about 5 weight percent Al₂O₃. For example,the fibers can contain about 70 to about 80 weight percent SO₂, about 18to about 27 weight percent MgO, and less than about 4 weight percent ofother trace elements. Suitable biosoluble inorganic oxides fibers aredescribed in U.S. Pat. No. 5,332,699 (Olds et al.); U.S. Pat. No.5,585,312 (Ten Eyck et al.); U.S. Pat. No. 5,714,421 (Olds et al.); andU.S. Pat. No. 5,874,375 (Zoitas et al.); and European Patent Application02078103.5, filed on Jul. 31, 2002. Various methods can be used to formbiosoluble inorganic fibers including, but not limited to, sol gelformation, crystal growing processes, and melt forming techniques suchas spinning or blowing.

Biosoluble fibers are commercially available from Unifrax Corporation,Niagara Falls, N.Y. under the trade designations “ISOFRAX” and“INSULFRAX.” Other biosoluble fibers are sold by Thermal Ceramics,Augusta, Ga., under the trade designation “SUPERWOOL.” For example,“SUPERWOOL 607” fiber contains 60 to 70 weight percent SiO₂, 25 to 35weight percent CaO, 4 to 7 weight percent MgO, and a trace amount ofAl₂O₃. “SUPERWOOL 607 MAX” fiber can be used at a slightly highertemperature and contains 60 to 70 weight percent Sift, 16 to 22 weightpercent CaO, 12 to 19 weight percent MgO, and a trace amount of Al₂O₃.

In a particular embodiment in connection with the present invention, theabove mentioned biosoluble fibers are used in combination with inorganicfibers, including heat treated glass fibers. When used in combinationwith one or more other inorganic fibers (i.e., non biosoluble fibers),the biosoluble fibers may be used in an amount between 97% and 10% basedon the total weight of inorganic fibers. In a particular embodiment theamount of biosoluble fibers is between 95% and 30% or between 85% and25%, based on the total weight of inorganic fibers.

The inorganic fibers for use with the present method typically have anaverage diameter of from about 1 micrometers to 50 micrometers, morepreferably about from 2 micrometers to 14 micrometers, and mostpreferably from 4 micrometers to 8 micrometers. When the inorganicfibers have an average diameter less than about 4 micrometers, theportion of respirable and potentially hazardous fibers may becomesignificant. In a particular embodiment, fibers having a differentaverage diameter may be combined to make a mounting mat. The presentmethod allows for easy and cost effective production of mounting matscomposed of fibers having different average diameters.

Furthermore, there is no specific limitation on the length of theinorganic fibers, similarly to the average diameter. However, theinorganic fibers typically have an average length of from about 0.01 mmto 1000 mm, and most preferably about 0.5 mm to 300 mm. In a particularembodiment, fibers having a different average length may be combined inmaking a mounting mat. For example, a mounting mat having a mixture ofshort and long fibers may be readily produced. In a particularembodiment, the mounting mat produced may include short fibers that havea length of not more than 15 mm and long fibers that have a length of atleast 20 mm and wherein the amount of short fibers is at least 3% byweight, based on the total weight of the mixture of long and shortfibers. Mounting mats composed of a mixture of long and short fibers inparticular include those that have a mixture of long and short glassfibers of the compositions described above. Mounting mats of short andlong fibers may have particular advantages, in particular, the coldholding power may be improved and good results can be achieved in a hotvibration test. The present method offers a way to produce these mats ina reliable, reproducible way and low cost and at performance levelsequal to or improved to those disclosed in the art.

The present invention includes non-intumescent as well as intumescentmounting mats of a large variety of compositions. An intumescent mat isa mat that contains an intumescent material. As used herein,“intumescent material” means a material that expands, foams, or swellswhen exposed to a sufficient amount of thermal energy. As used herein,“non-intumescent mat” means a mat that does not contain any intumescentmaterial or at least not enough of an intumescent material to contributea significant amount to the holding pressure exerted by the mountingmat.

Useful intumescent materials for use in making an intumescent matinclude, but are not limited to, unexpanded vermiculite ore, treatedunexpanded vermiculite ore, partially dehydrated vermiculite ore,expandable graphite, mixtures of expandable graphite with treated oruntreated unexpanded vermiculite ore, processed expandable sodiumsilicate, for example, that is commercially available under the tradedesignation “EXPANTROL” (insoluble sodium silicate), from 3M Company,St. Paul, Minn., and mixtures thereof. For purposes of the presentapplication, it is intended that each of the above-listed examples ofintumescent materials are considered to be different and distinguishablefrom one another. Desired intumescent materials include unexpandedvermiculite ore, treated unexpanded vermiculite ore, expandablegraphite, and mixtures thereof. An example of a desirable commerciallyavailable expandable graphite material is available under the tradedesignation “GRAFOIL” (Grade 338-50 expandable graphite flake), fromUCAR Carbon Co., Inc., Cleveland, Ohio.

The mounting mats in accordance with the present invention may beproduced by methods known in the art to produce mounting mats. In apreferred embodiment, the mats are readily produced in a cost effectiveway in accordance with the third aspect of the invention disclosedabove. This method of making mounting mats typically provides one ormore of the following advantages. Typically, the method allows toproduce mounting mats of a wide variety of compositions in a costeffective and convenient way. In particular, the method allows easymanufacturing of mounting mats including the nanoparticles and that haveno or low organic binder content. In particular the method allows toproduce the nanoparticle containing mats, including intumescent as wellas non-intumescent mats, with no or little binder in an easy,convenient, cost effective and reliable way leading to a consistentquality and performance.

In accordance with the method of the third aspect of the invention,fibers are supplied to a forming box through a fiber inlet of theforming box. A suitable forming box for use in connection with theinvention has been disclosed in WO 2005/044529, published May 19, 2005.The forming box includes a plurality of fiber separating rollersarranged in a row and that break apart clumps of fibers. Typically, thefiber separating rollers are spike rollers. The endless belt screenarranged in the forming box has an upper run, which runs immediatelybelow and/or above a row of spike rollers (i.e., for instance betweentwo rows of spike rollers and a lower run in the lower part of theforming box). Accordingly, fiber lumps or oversized fibers are preventedfrom being laid down on the forming wire and retained on the belt screenin the forming box and transported away from the lower portion of theforming box and returned to the spike rollers for furtherdisintegration. In an embodiment, the endless belt screen provides asieve or fiber screen member which is self-cleaning since the oversizedfibers are retained on one upper side of the lower run of the endlessbelt screen and released on lower side of the upper run of the endlessbelt screen because of the vacuum underneath the forming box and theforming wire.

In an embodiment, two rows of spike rollers are provided on each side ofthe upper run of the belt screen. Hereby, an initial disintegration ofthe supplied fibers may be provided before the screening by the beltscreen and a further disintegration after this first screening. In afurther embodiment, the spike rollers in the row immediately below theupper run of the belt screen are positioned with a decreasing distancebetween their axis of rotation and the belt screen in the direction oftravel of the upper run of the belt screen. Hereby, the fiber lumps orclusters of fibers retained on the lower run of the belt screen aregradually re-disintegrated as these retained fibers are returned to theupper part of the belt screen for reprocessing. By starting with a“course” processing of the returned fibers and then gradually reducingthe size of the gap between the belt screen and the individual spikerollers, it can be ensured that a lump of returned fibers isdisintegrated and not compressed and drawn through a gap between twoadjacent spike rollers. Hereby, a better disintegration may be achieved.In order to achieve further disintegration of the fibers and therebymore even distribution, two further rows of spike rollers may beprovided on each side of the lower run of the belt screen.

In an embodiment of the invention, the spike rollers are provided alongat least one of the vertical runs of the belt screen. Hereby, fibersthat are drawn along the belt screen may be re-processed also during thereturn path and/or the belt screen may be cleaned by the spike rollersprovided along the vertical path of the belt screen. In an embodiment ofthe invention, the belt screen extends beyond the housing in thedownstream direction with respect to the travelling direction of theforming wire. Alternatively, the belt screen is provided inside thehousing.

The belt screen may be driven with the same or in the opposite directionof movement of the lower run as the underlying forming wire. Moreover,the belt screen may be either continuously driven, (e.g., with aconstant speed, or intermittently driven). In one embodiment, twofurther rows of spike rollers may be provided on each side of the lowerrun of the belt screen. The belt screen is preferably provided with gridopenings in a predetermined pattern.

In one embodiment, the belt screen may be a wire mesh having apredetermined mesh opening. In another embodiment, the belt screen hastransversely orientated grid members with openings in between. In anembodiment of the invention, the lower run of the belt screen isimmediately above the forming wire so that the belt screen makes contactwith the upper side of the fiber formation being air laid on the formingwire. Hereby, the vacuum is screened in some areas in the bottom openingof the forming box and a predetermined surface structure of the laidproduct may be achieved. These vacuum screened areas are determined bythe screen pattern of the belt screen.

In the following, an embodiment of a forming box for use in a preferredmethod of making the mounting mats is described in more detail withreference to FIGS. 1-3.

In FIG. 1 and FIG. 2, a forming box for use with the method is shown.The forming box comprises a housing 1 into which fibers 3 are suppliedfrom an inlet 2. The forming box is positioned above a forming wire 4onto which the fibers 3 are air laid due to a vacuum box 5 underneaththe forming wire 4 to form a fiberboard 6 in a dry forming process. InFIG. 1, the forming box is shown with the interior elements visible inthe housing. However, it is realised that the housing walls may be madeeither from transparent or opaque materials.

The fibers 3 are blown into the housing 1 of the forming box via theinlet 2. Inside the forming box a number of spike rollers 7 are providedin one or more rows, (e.g. 15 four rows of spike rollers 71, 72, 73,74as shown in FIGS. 1 and 2). In the housing, an endless belt screen 8 isalso provided. This endless belt screen 8 is provided with a conveyingpath including an upper run 85, a vertical section 88 where the beltscreen 8 moves in a downwards direction, a lower run 86 where the beltscreen 8 travels substantially parallel with the underlying forming wire5 and an upwardly oriented 20 run 87, as shown in FIG. 3.

Adjacent the upper run 85 of the belt screen 8, at least one row ofspike rollers 71 is provided. In the embodiment shown two upper rows ofspike rollers 71, 72 and two lower rows of spike rollers 73, 74 areprovided at different levels in the housing 1. The belt screen isarranged with an upper run path 85 between the two upper rows of spikerollers 71, 72 and the lower run path 86 between the lower rows of spikerollers 73, 74. The fibers 3 may be supplied into the housing 1 inlumps. The spike rollers 7 then disintegrate or shredder the lumps offibers 3 in order to ensure an even distribution of fibers 3 in theproduct 6 formed on the forming wire 5. The fibers pass the spikerollers 71 in the first row and then the belt screen 8 and the secondrow of spike rollers 72 as the fibers are sucked downwards in theforming box. In the lower run 86 of the belt screen 8, oversized fibersare retained on the belt screen 8 and returned to the upper section ofthe forming box for further disintegration. The retained fibers arecaptured on the top of the lower run 86 of the belt screen 8 which thenbecome the lower surface of the upper run 85 and the fibers are suck offthe belt screen 8 and the lumps of fibers are shredded by the spikerollers one more time.

As shown in FIG. 3, the row of spike rollers 72 immediately below theupper run 85 of the belt screen 8 in inclined. This row 72 receives theretained, “oversized” fibers being returned from the retention below. Inorder to ensure that the fibers 3 are shredded efficiently in this row72, the first spike rollers 72′, 72″, 72′, 72″ in the row 72 areprovided with different distances between the axis of rotation of theindividual spike rollers 72′, 72″, 72″, 72″ and the upper run 85 of thebelt screen 8. The first spike roller 72′ in the row is positioned withthe largest distance and gradually the subsequent spike rollers 72″, 72″and 72″ are positioned with closer distances, so that fibers in thelumps of returned, oversized fibers are “peeled” off gently whereby itis ensured that the lumps are shredded and disintegrated rather thanbeing sucked and dragged off the belt screen and in between two adjacentspike rollers.

The endless belt screen 8 includes closed portions 81 and openings 82provided in a predetermined pattern. Alternatively, the belt screen 8could be a wire mesh. By a particular pattern of openings 82 andclosures 81 of the belt screen 8, a predetermined surface pattern on thefiberboard 6 formed by the dry-forming process may be achieved byarranging the lower run 86 of the belt screen 8 so that it makes contactwith the top surface of the fibers which are laid on the forming wire 4.

In the vertically oriented paths of travel 87, 88, one or more spikerollers (not shown) may be provided adjacent the belt screen 8 forloosing fibers on the belt screen. The configuration of the spikerollers may be chosen in accordance with the kinds of fibers which areto be air-laid by the forming box.

The bottom of the forming box may be provided with a sieve 11 (notshown), and the belt screen 8 may accordingly be provided with brushmeans (not shown) for removing retained fibers. Hereby, the belt mayadditionally be used for cleaning a bottom sieve. The brush means may bemembers provided for sweeping the fibers off the upper side of the lowerrun path of the belt screen. Alternatively or in combination, the beltscreen may be provided with means for generating a turbulent airflowstirring up the retained fibers on the sieve. In this manner, a formingbox with a bottom sieve may be provided with a cleaning facility for thebottom sieve and the belt may additionally be used for preventing thatthe sieve is clogging up.

In the above illustrated embodiments, the inlet is shown positionedabove the belt screen and the spike rollers. However, it is realisedthat the inlet may be positioned below the upper run of the belt screen,and/or that a multiple of inlets may be provided, (e.g. for supplyingdifferent types of fibers to the forming box). The spike rollers andindeed the belt screen will then assist in mixing the fibers inside theforming box.

In accordance with a preferred method for making the nanoparticlecontaining mounting mats, the mat of fibers formed on the forming wireis transported out of the forming box and is then compressed to adesired thickness suitable for mounting the mounting mat in the housingof a catalytic converter. The mat should be restrained such that thecompressed state of the mounting mat is maintained during furtherhandling, processing (e.g., cutting into a desired shape and size) andmounting of the mat in the catalytic converter. In the manufacturing ofa catalytic converter or pollution control device, the mounting mat isdisposed in a gap between the housing or casing of the pollution controldevice and the pollution control element, also called monolith.Typically, the gap between the housing and the pollution control elementwill vary between 2 mm and 10 mm, for example, between 3 mm and 8 mm.The gap size may be constant or may vary along the circumference of thepollution control element depending on the particular design of thepollution control device.

In accordance with the present invention, in addition to supplyinginorganic fibers through an inlet of the forming box, further desiredadjuvants used in the composition of the mounting mat may also besupplied through the inlet. In particular, the nanoparticles may besupplied through an inlet of the forming box. Further, in a particularembodiment, intumescent material may be included in and distributed inthe fiber mat by supplying the intumescent material through an inlet ofthe forming box, similar to the way the inorganic fibers is supplied tothe forming box. Accordingly, the present method enables the making ofan intumescent mat in an easy way at low cost and with a reproducibleand consistent performance, even at low binder content. Thus, thepresent method enables the making of intumescent mounting mats thatcontain no organic binder (e.g., that are needle punched) or that havean organic binder content of not more than 5% by weight, based on theweight of the mounting mat.

The inorganic nanoparticles may also be included in the mounting mat byspraying a dispersion thereof in a suitable liquid such as water or analcohol onto the fibers before or during forming of the mat. Stillfurther, the nanoparticles may be sprayed after forming the mat beforeor after compression thereof.

In FIG. 4 there is illustrated an embodiment of a pollution controldevice. Pollution control device 10 comprises a casing 11, typicallymade of a metal material, with generally frusto-conical inlet and outletends 12 and 13, respectively. Disposed within casing 11 is a pollutioncontrol element or monolith 20. Surrounding pollution control monolith20 is mounting mat 30 produced in accordance with the present method andwhich serves to tightly but resiliently support monolithic element 20within the casing 11. Mounting mat 30 holds pollution control monolith20 in place in the casing and seals the gap between the pollutioncontrol monolith 20 and casing 11 to thus prevent or minimize exhaustgases from by-passing pollution control monolith 20. As can be seen fromFIG. 4, the exterior of casing 11 is exposed to the atmosphere. In otherwords, the device 10 does not include another housing in which thecasing 11 is housed. In another embodiment however, the pollutioncontrol monolith may be held in a casing and one or more of these maythen be housed in a further casing as may be the case for example incatalytic converters for trucks. The casing of a pollution controldevice can be made from materials known in the art for such useincluding stainless steel, etc.

Pollution control elements that can be mounted with the mounting matinclude gasoline pollution control monoliths as well as diesel pollutioncontrol monoliths. The pollution control monolith may be a catalyticconverter, a particulate filter or trap, or the like. Catalyticconverters contain a catalyst, which is typically coated on a monolithicstructure mounted within a metallic housing. The catalyst is typicallyadapted to be operative and effective at the requisite temperature. Forexample for use with a gasoline engine the catalytic converter should beeffective at a temperature of 400° C. to 950° C. whereas for a dieselengine lower temperatures, typically not more than 350° C. are common.The monolithic structures are typically ceramic, although metalmonoliths have also been used. The catalyst oxidizes carbon monoxide andhydrocarbons and reduces the oxides of nitrogen in exhaust gases tocontrol atmospheric pollution. While in a gasoline engine all three ofthese pollutants can be reacted simultaneously in a so-called “three wayconverter”, most diesel engines are equipped with only a dieseloxidation catalytic converter. Catalytic converters for reducing theoxides of nitrogen, which are often used in diesel trucks today,generally consist of a separate catalytic converter.

Examples of pollution control monoliths for use with a gasoline engineinclude those made of cordierite that are commercially available fromCorning Inc., Corning, N.Y. or NGK Insulators, LTD., Nagoya, Japan ormetal monoliths commercially available from Emitec, Lohmar, Germany. Foradditional details regarding catalytic monoliths see, for example,“Advanced Ceramic Substrate: Catalytic Performance Improvement by HighGeometric Surface Area and Low Heat Capacity,” Umehara et al., Paper No.971029, SAE Technical Paper Series, 1997; “Systems Approach to PackagingDesign for Automotive Catalytic Converters,” 10 Stroom et al., Paper No.900500, SAE Technical Paper Series, 1990; “Thin Wall Ceramics asMonolithic Catalyst Supports,” Howitt, Paper 800082, SAE Technical PaperSeries, 1980; and “Flow Effects in Monolithic Honeycomb AutomotiveCatalytic Converters,” Howitt et al., Paper No. 740244, SAE TechnicalPaper Series, 1974.

Diesel particulate filters or traps are typically wall flow filters,which have honeycombed, monolithic structures typically made from porouscrystalline ceramic materials. Alternate cells of the honeycombedstructure are typically plugged such that exhaust gas enters in one celland is forced through the porous wall to an adjacent cell where it canexit the structure. In this way, the small soot particles that arepresent in diesel exhaust gas are collected. Suitable diesel particulatefilters made of cordierite are commercially available from Corning Inc.,Corning N.Y., and NGK Insulators Inc., Nagoya, Japan. Diesel particulatefilters made of Silicon Carbide are commercially available from IbidenCo. Ltd., Japan and are described in, for example, JP 2002047070A,published Feb. 12, 2002.

The mounting mat can be used to mount so-called thin wall or ultra-thinwall pollution control monoliths. In particular, the mounting mat can beused to mount pollution control monoliths that have from 400 cpsi (62cells per square centimeter (cpscm) to 1200 cpsi (186 cpscm) and thathave wall thickness of not more than 0.005 inch (0.127 mm). Examples ofpollution control monoliths that may be mounted with the mounting matinclude thin wall monoliths 4 mil/400 cpsi (102 micrometers/62 cells persquare centimeter (cpscm) and 4 mil/1600 cpsi (102 micrometers/148cpscm) and ultra-thin wall monoliths 3 mil/600 cpsi (76 micrometers/93cpscm), 2 mil/900 cpsi (51 micrometers/140 cpscm) and 2 mil/1200 cpsi(51 micrometers/186 cpscm).

The fiber mat may be compressed and restrained in a number of differentways including needling, stitch-bonding, resin bonding, applyingpressure and/or combinations thereof. Preferably, the compressed andrestrained fiber mat has a weight per unit area value in the range fromabout 800 g/m² to about 3000 g/m², and in another aspect a thickness inthe range from about 0.5 cm to about 3 cm. Typical bulk density under a5 kPA load is in the range 0.1 g/cm³ to 0.2 g/cm³. A mat containingintumescent materials may have a weight per area in the range from about2000 to 8000 g/m² and/or a bulk density under a 5 kPa load in the rangeof 0.3 g/cm³ to 0.7 g/m².

In one embodiment the fiber mat is compressed and restrained by needlepunching. A needle punched mat refers to a mat wherein there is physicalentanglement of fibers provided by multiple full or partial (preferably,full) penetration of the mat, for example, by barbed needles. The fibermat can be needle punched using a conventional needle punching apparatus(e.g., a needle puncher commercially available under the tradedesignation “DILO” from Dilo, Germany, with barbed needles (commerciallyavailable, for example, from—Beckert-Albstadt, Germany) to provide aneedle-punched fiber mat. Needle punching, which provides entanglementof the fibers, typically involves compressing the mat and then punchingand drawing barbed needles through the mat. The optimum number of needlepunches per area of mat will vary depending on the particularapplication. Typically, the fiber mat is needle punched to provide about1 to about 60 needle punches/cm². Preferably, the mat is needle punchedto provide about 5 to about 20 needle punches/cm².

The fiber mat can be stitchbonded using conventional techniques (seee.g., U.S. Pat. No. 4,181,514 (Lefkowitz et al.), the disclosure ofwhich is incorporated herein by reference for its teaching ofstitchbonding nonwoven mats). Typically, the mat is stitchbonded withorganic thread. A thin layer of an organic or inorganic sheet materialcan be placed on either or both sides of the mat during stitchbonding toprevent or minimize the threads from cutting through the mat. Where itis desired that the stitching thread not decompose in use, an inorganicthread, such as ceramic or metal (e.g., stainless steel) can be used.The spacing of the stitches is usually from 3 mm to 30 mm so that thefibers are uniformly compressed throughout the entire area of the mat.

In another embodiment, the mat may be compressed and restrained throughresin bonding. Typically, in resin bonding, the mat is impregnated orsaturated with an organic binder solution, compressed by apply pressureand the solvent of the binder solution is then removed such that themethod is retained at about its compressed thickness. As the organicbinder, any binders composed of an organic compound can be usable in thepresent method without particular limitations, as far as the binders canmaintain the compressed thickness of the compressed mat at an ordinarytemperature, and the thermal decomposition thereof permits restorationof the original thickness of the mat. It is preferred that the organicbinder be readily thermally decomposed and dissipated (destroyed) fromthe mat at a temperature at which the catalytic converter is intended tobe used. Further, since the mounting is exposed generally to atemperature of not less than 300° C. or to a temperature of 900° C. to1000° C. for a high-temperature use, it is preferred that the organicbinder be thermally decomposed for a short period of time so as to loseits function as a binder at a temperature of about 500° C. or lower.More preferably, the organic binder is dissipated at the temperaturerange from the mat upon the thermal decomposition.

As the organic binders, various rubbers, water-soluble polymercompounds, thermoplastic resins, thermosetting resins or the like areexemplified. Examples of the rubbers include natural rubbers; acrylicrubbers such as copolymers of ethyl acrylate and chloroethyl-vinylether, copolymers of n-butyl acrylate and acrylonitrile or the like;nitrile rubbers such as copolymers of butadiene and acrylonitrile or thelike; butadiene rubbers or the like. Examples of the water-solublepolymer compounds include carboxymethyl cellulose, polyvinyl alcohol orthe like. Examples of the thermoplastic resins include acrylic resins inthe form of homopolymers or copolymers of acrylic acid, acrylic acidesters, acrylamide, acrylonitrile, methacrylic acid, methacrylic acidesters or the like; an acrylonitrile-styrene copolymer; anacrylonitrile-butadiene-styrene copolymer or the like. Examples of thethermosetting resins include bisphenol-type epoxy resins, novolac-typeepoxy resins or the like.

The afore-mentioned organic binders may be used in the form of anaqueous solution, a water-dispersed emulsion, a latex or a solutionusing an organic solvent. These organic binders are hereinafter referredto generally as a “binder liquid”.

Resin bonding may also be accomplished by including a polymeric materialfor example in the form of a powder or fiber into the mat, compressingthe mat by exerting pressure thereon and heat treating the compressedmat so as to cause melting or softening of the polymeric materialthereby bonding fibers in the mat and thus restraining the mat uponcooling.

Suitable polymeric materials that may be included in the mat includethermoplastic polymers including polyolefines, polyamides, polyesters,vinyl acetate ethylene copolymers and vinylester ethylene copolymers.Alternatively, thermoplastic polymeric fibers may be included in themat. Examples of suitable thermoplastic polymeric fibers includepolyolefin fibers such as polyethylene, or polypropylene, polystyrenefibers, polyether fibers, polyester fibers such as polyethyleneterephthalate (PET) or polybutaline terephthalate (PBT), vinyl polymerfibers such as polyvinyl chloride and polyvinylidene fluoride,polyamides such as polycaprolactame, polyurethanes, nylon fibers andpolyaramide fibers. Particularly useful fibers for thermal bonding ofthe fiber mat include also the so-called bicomponent fibers whichtypically comprise polymers of different composition or with differentphysical properties. Typically, these fibers are core/sheath fiberswhere for example the polymeric component of the core provides structureand the sheath is meltable or thermoplastic enabling bonding of thefibers. For example, in one embodiment, the bicomponent fiber may be acore/sheath polyester/polyolefin fiber. Bicomponent fibers that can beused include those available under the trade designation “TREVIRA 255”from Trevira GmbH, Bobingen, Germany and “FIBERVISION CREATE WL” fromFiberVisions a/s, Varde, Denmark.

In a particular embodiment, two or more fiber mat layers (one or both ofwhich may contain nanoparticles) may be formed on top of one another.For example, in one embodiment of such co-forming, the method comprisesforming a first mat of fibers by performing steps (i) to (iv) of themethod described above, forming at least one second mat of fibers on thefirst mat by repeating steps (i) to (iv) with the first mat beingprovided on the forming wire and carrying out step (v) of the method(i.e. compressing and restraining) so as to obtain a mounting having afirst and second mat of fibers. According to an alternative embodiment,the first mat of fibers is first compressed and restrained beforeforming the second mat layer thereon.

For particular formulations or compositions of mounting mat, it may bedesired to stabilize the mounting mat. Such may be particularlydesirable for mounting mats that have a low organic binder content ornone at all or that have unbonded particulate material distributed inthe fiber mat. For example, in one embodiment to stabilize the mountingmat, it may be desirable to coat or impregnate the surface on one orboth sides of the mounting mat by spraying thereon an organic bindersolution. According to another embodiment, a fiber mat may be co-formedon one or both sides of a mounting mat (using a method of coforming asdescribed above) that contains no or little organic binder and/or thatcontains particulate material distributed therein. The fiber mats thatare being coformed on either or both sides of such a mat may contain arelatively large proportion of thermoplastic polymer material in theform of powder or fiber. Following heating, this polymeric material iscaused to melt, thereby forming a fiber mat layer on either or bothsides that may protect dislodging of fibers or loss of particulatematerial during handling of the mounting mat.

In a particular embodiment in connection with the present invention themounting mat may include one or more further layers. In particular, themounting mat may contain one or more layers selected from the groupconsisting of scrims and nettings. The scrim or netting typically is athin layer having an area weight of between 10 g/m² and 150 g/m², forexample between 15 g/m² and 100 g/m² or between 20 g/m² and 50 g/m².Generally the weight of the scrim or netting in a mounting mat is smallcompared to the overall weight of the mounting mat. Generally, theweight percentage of a netting or scrim in the mounting mat is between1% and 10% by weight, for example between 2% and 6% by weight. A nettingfor use in connection with the present invention typically comprisespolymeric fibers and/or inorganic fibers arranged in a generally regularway. For example, in one embodiment, the fibers may be parallel to eachother. In another embodiment, fibers may be arranged in parallel in twoorthogonal directions thereby crossing each other and defining square orrectangular spaces between them. A scrim for use in connection with thepresent invention typically is a non-woven having a random orientationof fibers. The fibers of a scrim may contain any of the inorganic fibersdisclosed above as well as any type of polymeric fibers, in particularthe thermoplastic polymeric fibers disclosed above.

In one embodiment, a layer of scrim or netting may be included withinthe body of the mounting mat for the purpose of reinforcing the mountingmat.

In a still further embodiment, a scrim layer or netting may be providedon one or both sides of the mounting mat. Conveniently, this can be doneby supplying the scrim or netting on the forming wire of forming machinedescribed above. A further scrim or netting may be provided on theformed fiber mat if needed or desired and the mat and scrim(s) ornetting(s) may then be needle punched or stitchbonded together.According to a further embodiment, the scrim or scrims (or netting ornettings) may be coated with an organic binder material or thescrim/netting itself may comprise thermoplastic polymeric fibers.Accordingly, following a subsequent heat treatment, the organic binderor thermoplastic fibers may form a film or bond to the fibers of thefiber mat.

In a particular embodiment, an organic binder is applied on one or bothsides of the mat to reduce or minimize fiber shedding. Such an organicbinder may be powder coated or sprayed on one or both opposite majorsurfaces of the mat for a solution or dispersion in an appropriateliquid medium. Furthermore, as described below, the coating so appliedmay be selected so as to also adjust the frictional properties of themat.

In a particular embodiment of the present invention, the mounting matsmay be impregnated. In one embodiment, the fibers of the fiber mat areimpregnated with one or more of an organosilicon compound selected fromthe group consisting of siloxane compounds, preferably silsesquioxanes,hydrolysates and condensates, preferably self-condensates, of thesecompounds, and combinations thereof. A hydrolysate and/or a condensate,particularly a self-condensate, of a siloxane compound sometimes can beformed, for example, in an aqueous solution of said siloxane, inparticular, if said aqueous solution is not immediately but only somehours later applied. The siloxane compound, after drying, generallyforms a very thin continuous or discontinuous coating on the fibers.Examples of siloxane compounds which can be used for impregnating thefibers are organosiloxanes such as silsesquioxanes, copolymers(co-condensates) thereof and hydrolysates thereof, polyorganosiloxanessuch as polydiorganosiloxanes, and hydrolysates thereof, andcombinations thereof. In a particular embodiment, the organosiloxane(e.g., the silsesquioxane or the polyorganosiloxane) comprises one ormore functional groups which are capable for a self-condensationreaction under the desired impregnation conditions, such as a hydroxygroup, an alkoxy group such as methoxy, ethoxy, propoxy, butoxy, and thelike known functional groups for a self-condensation reaction. Suchgroups are preferably positioned at a terminal position of theorganosiloxane, but can also be located on a side chain, preferably atthe terminal position thereof. Particularly preferable aresilsesquioxanes as described below, preferably having one or morefunctional groups for a self-condensation reaction, as mentioned above,at a terminal position of the main chain or a side chain.

The term “silsesquioxanes” (also referred to as silasesquioxanes) asused herein includes silsesquioxanes as well as silsesquioxanecopolymers (co-condensates). Silsesquioxanes per se are silicon-oxygencompounds wherein each Si atom is bound to an average of 3/2 (sesqui) Oatoms and to one hydrocarbon group, having the general formula (I)

R_(2n)Si_(2n)O_(3n)  (I)

-   -   wherein    -   R is H or an organic residue having preferably from 1 to 20,        more preferably, 1 to 12 carbon atoms, and    -   n is an integer of 1 to 20, preferably 2 to 15, more preferably,        3 to 12, and even more preferably, 4 to 12. Preferably, the        silsesquioxane used for impregnating the fiber blanket is solid        at room temperature (23° C.±2° C.). Furthermore, the        silsesquioxane preferably comprises a functional group, such as        hydroxy or alkoxy group, at a terminal position, which can        self-crosslink under the desired impregnation conditions as        indicated below. They can in principle be obtained by e.g.        hydrolytic condensation of trifunctional (e.g.,        trialkoxy-functional) silanes (e.g., R—Si(OR)₃).

In the above formula (I), R is an organic group or substituted organicgroup preferably containing from 1 to 20, more preferably 1 to 12, evenmore preferably 1 to 8 carbon atoms, and optionally one or more,preferably 1 to 5, heteroatoms selected from nitrogen, oxygen andsulfur, preferably nitrogen and oxygen. R of the silsesquioxane can bean alkyl, alkenyl, alkynyl, cycloalkyl, aryl, alkaryl or an aralkylgroup, and these groups optionally can contain 1 to 5 heteroatoms suchas nitrogen or oxygen. These groups optionally can contain one or moresubstituents such as amino, mercapto, hydroxyl, alkoxy, epoxy, acrylato,cyano and carboxy groups, wherein preferred substituents are amino,mercapto, epoxy or C₁-C₈-alkoxy groups.

Specific illustrative examples of R are C₁-C₈-alkyl such as methyl,ethyl, propyl, butyl, pentyl, hexyl, and heptyl; C₂-C₈-alkenyl such asvinyl, allyl, butenyl and hexenyl; C₂-C₈-alkynyl such as ethinyl andpropinyl; C₃-C₈-cycloalkyl such as cyclopentyl, cyclohexyl andcycloheptyl; C₁-C₈-alkoxy such as methoxy, ethoxy, propoxy, butoxy,pentoxy and hexoxy; C₂-C₈-alkenoxy such as ethylenoxy, propylenoxy andbutylenoxy; propargyl; optionally substituted aryl having 6 to 12 carbonatoms such as phenyl, tolyl, benzyl and naphthyl; R¹—(O—R²)_(n)— orR³—(NR⁵—R⁴)_(n)—, wherein R¹ to R⁴ is independently an optionallysubstituted, saturated or unsaturated hydrocarbon group having up to 8carbon atoms, preferably selected from the groups as mentioned above, R⁵is hydrogen or C₁-C₈ alkyl and n is 1 to 10; and all representatives ofthe above mentioned groups substituted by one or more amino, hydroxyl,mercapto, epoxy or C₁-C₈-alkoxy groups. From the above mentioned groups,optionally substituted C₁-C₈-alkyl, optionally substituted aryl having 6to 12 carbon atoms, and R¹—(O—R²)_(n)— or R³—(NR⁵—R⁴)_(n)—, wherein R¹to R⁴ is independently an optionally substituted, saturated orunsaturated hydrocarbon group having up to 8 carbon atoms, preferablyselected from the groups as mentioned above, R⁵ is hydrogen or C₁-C₈alkyl and n is 1 to 10, wherein the optional substituent is selectedfrom amino, hydroxyl, mercapto, epoxy or C₁-C₈-alkoxy groups, isparticularly preferred.

Further illustrative examples of the R are 3,3,3-trifluoropropyl,dichlorophenyl, aminopropyl, aminobutyl, H₂NCH₂CH₂NH(CH₂)₃—,

-   -   H₂NCH₂CH₂NHCH₂CH(CH₃)CH₂—, mercaptopropyl, mercaptoethyl,        hydroxypropyl,

-   -   CH₂—CHCOO(CH₂)₃—, CH₂═C(CH₃)COO(CH₂)₃—, cyanopropyl, cyanoethyl,        carboxyethyl and carboxyphenyl groups. Of course, the        substituents on the hydrocarbon residues should not be reactive        with water. The methyl, ethyl, propyl, the aminomethyl,        aminoethyl and aminopropyl, and mercaptoethyl and mercaptopropyl        groups are preferred when a single silsesquioxane is used. When        R is other than a methyl or mercaptopropyl it is preferred that        the silsesquioxane be copolymerized with methyl silsesquioxane        in a weight ratio of from 5 to 30:70 to 95, i.e., 5 to 30% by        weight of RSiO_(3/2) units and 70 to 95% by weight of        CH₃SiO_(3/2) units.

Silsesquioxanes that may be used in the present invention generally havea low average molecular weight (Mw), wherein Mw preferably is in therange of up to 10,000, preferably, 200 to 6000 and still more preferably250 to 5000 and 300 to 4000, determined by Gel Permeation Chromatography(GPC) using a polystyrene standard. GPC test methods are furtherexplained in “Modern Size Exclusion Liquid Chromatography” Practice ofGel Permeation Chromatography, John Wiley and Sons, 1979. Usefulsilsesquioxanes are described in U.S. Pat. No. 3,493,424 (Mohrlok etal.); U.S. Pat. No. 4,351,736 (Steinberger et al.); and U.S. Pat. No.4,781,844 (Kortmann et al.), each incorporated herein by reference.

Silsesquioxane copolymers (co-condensates) include copolymers orco-condensates of silsesquioxane polymers of the formula R¹¹SiO_(3/2) orof R¹¹—Si(OR¹²)₃ with diorganooxysilanes (or hydrosylates thereof) ofthe formula R¹¹ ₂Si(OR¹²)₂ and/or tetraorganooxysilanes (or hydrosylatesthereof) of the formula Si(OR¹²)₄ wherein each R¹¹ is as defined abovefor group R and preferably each R¹¹ represents an unsubstituted orsubstituted hydrocarbon radical having 1 to 12, preferably 1 to 8 carbonatoms, substituents of which may be amino, mercapto and epoxy groups,and R¹² is independently an alkyl group of 1 to 8, preferably 1 to 4carbon atoms. The silsesquioxane may optionally further comprise aco-condensate of silanes of the formula R¹¹ ₃SiOR¹². Preferredsilsesquioxane polymers are neutral or anionic. Useful silsesquioxanescan be made by the techniques described in U.S. Pat. No. 3,493,424(Mohrlok et al.), U.S. Pat. No. 4,351,736 (Steinberger et al.), U.S.Pat. No. 5,073,442 (Knowlton et al.), and U.S. Pat. No. 4,781,844(Kortmann et al).

Mixtures of silsesquioxanes and of silsesquioxane copolymers can also beemployed, if desired. The silsesquioxane should typically be solid, i.e.it is neither gaseous nor liquid at room temperature (23° C.±2° C.). Thesilsesquioxanes can be used as colloidal suspension. The silsesquioxanesmay be prepared by adding silanes to a mixture of water, a buffer, asurfactant and optionally an organic solvent, while agitating themixture under acidic or basic conditions. The surfactant used in thesilsesquioxane preparation should be either anionic or cationic innature. Best results are generally obtained with the cationicsuspensions. It is preferable to add the quantity of silane uniformlyand slowly in order to achieve a narrow particle size. The averageparticle size of the silsesquioxanes in the colloidal suspension shouldbe within the range of 1 nm to 100 nm (10 Angstroms to 1000 Angstroms),preferably in the range of 1 nm to 50 nm (10 Angstroms to 500 Angstroms)or in the range of 1 nm to 40 nm (10 Angstroms to 400 Angstroms), andmore preferably in the range of 20 nm to 50 nm (200 Angstroms to 500Angstroms). The exact amount of silane that can be added depends on thesubstituent R and whether an anionic or cationic surfactant is used.

Silsesquioxane copolymers in which the units can be present in block orrandom distribution are formed by the simultaneous hydrolysis of thesilanes. The preferred amount of the silanes of the formula Si(OR²)₄,including hydrosylates thereof (e.g. of the formula Si(OH)₄), added is 2to 50 wt. %, preferably 3 to 20 wt. %, relative to the weight of thesilanes employed. The amount of tetraorganosilanes, includingtetraalkoxysilanes and hydrosylates thereof (e.g. of the formulaSi(OH)₄) present in the resulting composition is preferably less than 10wt. %, preferably less than 5 wt. %, more preferably less than 2 wt. %relative to the weight of the silsesquioxane.

The following silanes are e.g. useful in preparing the silsesquioxanesof the present invention: methyltrimethoxysilane, methyltriethoxysilane,methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,propyltrimethoxysilane, isobutyltrimethoxysilane,isobutyltriethoxysilane, 2-ethylbutyltriethoxysilane, tetraethoxysilaneand 2-ethylbutoxytriethoxysilane.

Preferably, the hydroxy number is from about 1000 to 6000 per gram, andis more preferably from about 1500 to 2500. The hydroxy number may bemeasured, for example, by titration or the molecular weight may beestimated by ²⁹Si NMR.

A useful silsesquioxane containing essentially no residualtetraalkyoxysilanes (or hydrosylates thereof such as Si(OH)₄) (availableunder the trade designation “SR 2400 RESIN” from Dow Corning, Midland,Mich.). A particularly preferred example of a silsesquioxane isavailable under the trade designation “DRI-SIL 55” from Dow Corning,which is 98 wt. % (3-(2-aminoethyl)aminopropyl)-methylsesquioxane havingmethoxy at the terminus, in methanol.

In a further embodiment, the siloxane compound is a polyorganosiloxane,preferably a polydiorganosiloxane. Preferably, the polyorganosiloxaneused for impregnating the fiber mat is solid at room temperature (23°C.±2° C.). Furthermore, the polyorganosiloxane preferably comprises afunctional group, such as hydroxy or alkoxy, at a terminal position,which can self-crosslink under the desired impregnation conditions asindicated below. Polyorganosiloxanes preferably used in the presentinvention have a low average molecular weight (Mw), wherein Mwpreferably is in the range of up to 10,000, preferably, 200 to 6000 andstill more preferably, 250 to 5000 and 300 to 4000, determined by GelPermeation Chromatography (GPC) using a polystyrene standard. Forexample, a polyorganosiloxane, preferably a polydiorganosiloxane, can beused in which at least about 50% of the total silicon-bondedsubstituents are methyl groups and any remaining substituents are othermonovalent hydrocarbon groups such as the higher alkyl groups (having,for example, 4 to 20 carbon atoms), for example, tetradecyl andoctadecyl, phenyl groups, vinyl groups and allyl groups, and monovalenthydrocarbonoxy and substituted hydrocarbon groups, for example, alkoxygroups, alkoxy-alkoxy groups, fluoroalkyl groups, hydroxyalkyl groups,aminoalkyl and polyamino(alkyl) groups, mercaptoalkyl groups andcarboxyalkyl groups. Specific examples of such hydrocarbonoxy andsubstituted hydrocarbon groups are methoxy, ethoxy, butoxy,methoxyethoxy, 3,3-trifluoro-propyl, hydroxymethyl, aminopropyl,beta-aminoethyl-gamma-aminopropyl, mercaptopropyl and carboxybutyl. Inaddition to the aforementioned organic substituents the organosiloxanemay have silicon-bonded hydroxyl groups (normally present in terminalsilanol groups), or silicon-bonded hydrogen atoms as in, for example,the poly(methylhydrogen) siloxanes and copolymers of dimethylsiloxaneunits with methylhydrogensiloxane units and/or dimethylhydrogensiloxaneunits.

In some cases the polyorganosiloxane, such as the polydiorganosiloxane,may comprise two or more different types of siloxanes, or it may beemployed in conjunction with other organosilicon compounds. For example,the polyorganosiloxane may comprise both a silanol-terminatedpolydimethylsiloxane and a crosslinking agent therefore such as apoly(methylhydrogen) siloxane, an alkoxy silane (e.g., CH₃Si(OCH₃)₃and/or NH₂CH₂CH₂NH(CH₂)₃Si(OC₂H₅)₃) or partial hydrolysates andcondensates of such silanes. Thus, any of a wide range oforganosiloxanes may be employed as polyorganosiloxane depending on theproperties. Generally preferred as polyorganosiloxanes, e.g.,polydiorganosiloxanes, are polyorganosiloxanes having terminalsilicon-bonded reactive groups, for example, hydroxyl and alkoxy groups,employed either alone or in combination with other organosiloxanecompounds. The above polyorganosiloxane, e.g. a polydiorganosiloxane,can also be used in combination with an organosilane of the generalformula (II)

-   -   wherein each Y represents a monovalent group having less than 6        carbon atoms selected from hydrocarbon groups, alkoxy groups and        alkoxyalkoxy groups, at least one Y being alkoxy or        alkoxyalkoxy, R represents a divalent group having from 3 to 10        carbon atoms, the said group being composed of carbon, hydrogen        and, optionally, oxygen present in the form of ether linkages        and/or hydroxyl groups, R′ represents a monovalent hydrocarbon        group having from 1 to 15 carbon atoms or the group (—OQ)_(a)OZ,        wherein Q represents an alkylene group having 2 or 3 carbon        atoms, a has a value of from 1 to 20 and Z represents a hydrogen        atom, an alkyl group or an acyl group, each R″ represents a        methyl or an ethyl group and X represents a halogen atom.

In the above specified general formula (II) the divalent group R iscomposed of carbon and hydrogen or carbon, hydrogen and oxygen, anyoxygen being present in the form of ether linkages and/or hydroxylgroups. The group R may therefore be, for example, methylene, ethylene,hexylene, xenylene, —CH₂CH₂OCH₂CH₂— and —(CH₂)₂OCH₂CH(OH)CH₂—.Preferably, R represents the groups —(CH₂)₃—, —(CH₂)₄— or—CH₂CH(CH₃)CH₂—. The R′ group may be any monovalent hydrocarbon grouphaving from 1 to 15 carbon atoms, for example, an alkyl group, e.g.methyl, ethyl, propyl, butyl or tetradecyl, an alkenyl group, e.g.,vinyl, or an aryl, alkaryl or aralkyl group, e.g., phenyl, naphthyl,tolyl, 2-ethylphenyl, benzyl and 2-phenylpropyl. The R′ group may alsobe the group —(OQ)_(a)OZ as hereinabove defined, examples of such groupsbeing —(OCH₂CH₂)OH, —(OCH₂CH₂)₃OH, —(OCH₂CH₂)₃(OCH₂CH₂CH₂)₃OC₄H₉ and—(OCH₂CH₂)₂OC₃H₇. As the Y substituents there may be present monovalenthydrocarbon groups such as methyl, ethyl, propyl and vinyl, and alkoxyand alkoxyalkoxy groups, for example, methoxy, ethoxy, butoxy andmethoxyethoxy. At least one Y should be alkoxy or alkoxyalkoxy, thepreferred silanes being those wherein the Y substituents are selectedfrom methyl groups and alkoxy or alkoxyalkoxy groups having less than 4carbon atoms.

Preferably, X represents chlorine or bromine. The above organosilanesare known substances and can be prepared for example by the reaction ofa tertiary amine, for example, C₁₅H₃₁N(CH₃)₂, with a haloalkylsilane,for example, chloropropyltrimethoxy silane, or by the addition of anunsaturated amine to a hydrosilicon compound followed by reaction of theproduct with a hydrocarbyl halide or a hydrogen halide.

In a further embodiment of the invention, the fibers can be impregnatedwith an organosilicon compound selected from an alkoxy group-containingsilane, preferably an optionally substituted alkyl- oraryl-alkoxysilane, more preferably an optionally substituted alkyl- oraryl-trialkoxysilane of the formula RSi(OR′)₃, a hydrolysate and acondensate thereof, and combinations thereof. If R is alkyl, the alkylgroup preferably contains 1 to 20, more preferably, 1 to 16, even morepreferably, 1 to 10 or 1 to 8 carbon atoms. Preferred alkyl groups aremethyl, ethyl, propyl, methylethyl, butyl, pentyl, hexyl, andcyclohexyl. If R is aryl, the aryl group is preferably phenyl. Thealkoxy group OR′ preferably contains 1 to 12, more preferably, 1 to 8,even more preferably, 1 to 6 carbon atoms. Preferred alkoxy groups aremethoxy and ethoxy, also 2-methoxyethoxy and isopropoxy are useful. Thealkoxy groups are selected independently from each other. The optionalsubstituent is preferably selected from amino, optionally furthersubstituted with, for example, C₁-C₆-alkyl or amino-C₁-C₆-alkyl; epoxy,3-glycidyloxy, 3-(meth)acryloxy, mercapto and C₁-C₆-alkoxy groups. In apreferred embodiment only the alkyl group is substituted. A hydrolysateand/or a condensate, particularly a self-condensate, of such an alkoxygroup-containing silane compound can be formed, for example, in anaqueous solution of said silane, in particular, if said aqueous solutionis not immediately but only some hours later applied.

Examples of trialkoxysilanes are methyltrimethoxysilane,methyltriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane,ethyltriethoxysilane, propyltrimethoxysilane, isobutyltrimethoxysilane,isobutyltriethoxysilane, 2-ethylbutyltriethoxysilane, tetraethoxysilane,2-ethylbutoxytriethoxysilane, phenyltriethoxysilane,cyclohexyl-triethoxysilane, methacryloxytrimethoxysilane,glycidoxytrimethoxysilane, andN-(2-aminoethyl)-3-aminopropyltrimethoxysilane. Examples of alkyl- orphenyl-trialkoxysilanes are commercially available under the tradedesignation “DYNASYLAN” from Degussa, Frankfurt, Germany, an example ofwhich is “DYNASYLAN PTMO”, which is a propyltrimethoxysilane.

Impregnation materials also include blends of trialkoxysilanes asmentioned above with tetraalkoxysilanes of the formulae Si(OR)₄ orSi(OR)₃OR′ or Si(OR)₂(OR′)₂, wherein R and R′ are an optionallysubstituted alkyl group preferably, containing 1 to 20, more preferably,1 to 16, even more preferably, 1 to 10 or 1 to 8 carbon atoms. Preferredalkyl groups are methyl, ethyl, propyl, methylethyl, butyl, pentyl,hexyl, and cyclohexyl. The optional substituent is preferably selectedfrom amino, optionally further substituted with e.g. C₁-C₆-alkyl oramino-C₁-C₆-alkyl; epoxy, 3-glycidyloxy, 3-(meth)acryloxy, mercapto andC₁-C₆-alkoxy groups.

The mat may be impregnated with any of the above materials before orafter compression and restraining of the fiber mat. Still further, it isalso possible to impregnate the fibers before they are being supplied tothe forming box.

In a further embodiment, a thin continuous or discontinuous coating of ahigh friction coating material is formed on the internal surface (i.e.,the surface of the mounting mat to be contacted with the pollutioncontrol element) and optionally the external surface (i.e., the surfaceof the mounting mat to be contacted with the housing) of the mountingmat. The high friction coating is applied such that the high frictioncoating material does not essentially invade the mounting mat.Furthermore, the internal surface and optionally the external surface ofthe mounting mat is coated with a high friction coating such that thecoefficient of friction between the optionally coated external surfaceof the mounting mat and the housing is lower than the coefficient offriction between the coated internal surface of the fiber mat and thecatalyst element. The organic portion of the high friction coatingdecomposes and dissipates partly or completely under typical operatingconditions of the catalyst element. The high friction coating of theexternal surface can be the same as or can be different to the highfriction coating of the internal surface of the mounting mat. To obtainthe desired mounting characteristics, precaution must be taken so thatthere is a difference in the impregnation amount between the side of theexternal surface and the side of the internal surface of the mountingmat, if the same coating material is used on both surfaces. Forimpregnation with the same high friction coating, the solid componentcontent of the coating material with which the side of the internalsurface is impregnated should therefore be larger than that of thecoating material with which the side of the external surface isimpregnated. It has been shown that excellent stuffing results can beachieved when the friction difference between both sides is maximized.Although there is no specific restriction on the difference of thecontent of the high friction coating on the mounting mat, the solidcomponent content of the high friction coating on the side of theinternal surface of the mounting mat is preferably from about 5 g/m² to100 g/m², more preferably from about 20 g/m² to 50 g/m². On the otherhand, the solid component content of the high friction coating on theexternal surface of the mounting mat is preferably from about 0.5 g/m²to 10 g/m².

The high friction coating typically serves to improve the behaviour e.g.during the stuffing of catalyst, which is a commonly used canningmethod. The high friction coating is chosen to provide anti-skidproperties on the surface of the catalyst element to avoid slippage ofthe mat during canning. The coating can be selected from natural orsynthetic polymeric materials, preferably a resin or rubber materialsuch as an acrylic resin or rubber such as an acrylic acid estercopolymer, a nitrile resin or rubber, a vinylacetate copolymer, apolystyrene resin, an acrylate-styrene copolymer, a styrene-butadieneresin, a SIS block copolymer, an EPDM, an ABS, a PE or PP film, etc.,and combinations thereof. Many of these organic polymeric materialsprovide excellent anti-skid properties. Some of these organic polymerscan soften at elevated temperatures, which can lead to reduced holdingperformance in a certain temperature/time window before the organicpolymeric material degrades and disappears. Inorganic coatings such assilica-, alumina-, and clay-gels or particle slurries, etc. can be used,but may sometimes have lower anti-slip properties compared to organicpolymeric material. Their advantage is that they do not decompose athigher temperatures and therefore provide a permanent friction increaseleading to an increased mat holding performance. A further optimizationof the holding performance can be achieved by putting an inorganic highfriction coating on the housing side of the mat, which does not changethe stuffing performance significantly, but leads to increased frictionand mat holding performance.

In a particular embodiment the high friction coating composition iscomposed of a latex that can be decomposed and dissipated at arbitraryreactions taking place under high temperature conditions applicableduring operation of the catalytic converter. Usable latex hereinincludes a colloidal dispersion obtained by dispersing a natural orsynthetic polymer material, preferably a resin material such as anacrylic acid ester copolymer, a vinylacetate copolymer, a polystyreneresin, an acrylate-styrene copolymer, a styrene-butadiene resin, andcombinations thereof, into an aqueous medium or another medium, or anorganic material such as a poly(vinyl alcohol). Optionally, the latexfurther comprises in admixture thereto one or more of a silica-,alumina-, or clay particles. Acrylic latex for which an acrylic resin isused can be particularly advantageously used. Examples of preferredlattices are vinylacetate-ethylene polymer dispersion available underthe trade designation “AIRFLEX EAF67” from Air Products Polymers,Allentown, Pa., USA and aqueous, plasticizer-free dispersions of athermally crosslinkable copolymer of acrylic acid esters available underthe trade designations “ACRONAL A 420 S” and “ACRONAL LA 471 S” fromBASF, Ludwigshafen, Germany.

In a further embodiment, the high friction coating with which the fibermat is coated can also comprise the above described organic polymericmaterial and one or more types of abrasive particles. Further details,particularly with respect to useful organic polymeric materials anduseful abrasive particles can be found in WO-A-2006/020058, publishedFeb. 23, 2006. For example, a slurry prepared by dispersing fineparticles of an abrasive material in an organic polymeric material isapplied to the surface(s) of the fiber mat. There is thus obtained afiber mat having a coating in which fine particles of abrasivematerial(s) are selectively fixed at least on the internal surface andoptionally the external surface of the fiber mat. Because the fineparticles of the abrasive material are arranged at least on the contactsurface of the fiber mat with the catalyst element, the coefficient offriction with the catalyst element can be increased and retainingreliability of the catalyst element can be further improved.Furthermore, when the catalyst element and the fiber mat, which is woundaround the catalyst element, are canned, the movement between thecatalyst element and the wrapped fiber mat can be prevented, or at leastsignificantly reduced, without detrimentally affecting the ability ofthe catalytic converter to be assembled.

Coating of the mounting mat with a high friction coating as explainedabove, can be advantageously conducted with known conventionaltechnologies such as spraying, brushing, laminating, printing (e.g.,screen printing) and the like. A preferred method is spray coating byusing, for example, a lacquer spray system such as an air brush, whichis satisfactorily conducted by, for example, only preparing a spraysolution or dispersion and successively or simultaneously spraying thesolution or dispersion (e.g., the acrylic latex or the like lattices asmentioned above), on one or both main surfaces of the fiber mat. Theoperation is therefore simple and economical. The solution or dispersionsubsequent to spraying may be dried naturally or dried by heating to asuitable temperature (e.g., 110° C.). The solid component content of thehigh friction coating on the side of the internal surface of the fibermat is preferably from about 5 g/m² to 100 g/m², more preferably fromabout 10 g/m² to 50 g/m², and the solid component content of the highfriction coating on the external surface of the mounting mat ispreferably from about 0.5 g/m² to 10 g/m². Preferably, a thin continuousor discontinuous coating of the high friction coating material is formedon the internal and optionally the external surface of the mounting mat,respectively. The used coating method is adapted such that any capillaryactions of the mounting mat are minimized and that the high frictioncoating material does not essentially invade the mounting mat. That is,the high friction coating should substantially be present only on thesurface of the mounting mat and should not essentially infiltrate themat. This can be achieved by using, for example, coating solutions ordispersions having a high solids concentration, addition of emulsifyingagents or thixotropic agents or the like additives having similareffects to the solution or dispersion, coating the mounting mat, coatingconditions under which the used solvent rapidly evaporates and the like,or by lamination of the essentially solvent-free high friction coating.It is preferred that the high friction coating infiltrates less than10%, preferably, less than 5%, more preferably, less than 3% and mostpreferably, less than 1% of the thickness of the mounting mat.

EXAMPLES

The following examples further illustrate the present invention withoutthe intention to limit the invention thereto.

List of Materials

Trade Chemical State/ Designation Supplier Material Type CompositionDimensions ISOFRAX Unifrax Corp. HQ, Biosoluble Alkaline earth BulkFiber Niagara Falls, NY, Ceramic Fiber silicate, 75% USA SiO_(2,) 23%Mg0 SUPERWOOL Thermal Ceramics, HQ Biosoluble Alkaline earth Bulk Fiber607HT in Rueil, Malmaison, Ceramic Fiber silicate, 75% France SiO_(2,)23% CaO/Mg0 SAFFIL 3D+ Saffil Ltd., United Polycrystalline 96% Al₂O₃, 4%Kingdom Ceramic Fiber SiO₂ Silica Yarn Polotsk-Steklovolokno SilicaFiber 95% SiO₂ Chopped K11C6 Co., Belarus Fiber R-Glass St. GobainVetrotex, Glass Fiber 60% SiO₂, 25% Chopped Chambery, France Al₂O₃, 9%CaO, Fiber 6% MgO Vermiculite — Natural Mineral Magnesium Fine Particlesaluminium iron silicate mineral belCoTex belChem Co., Freiberg, SilicaFiber 95% SiO₂ Chopped Germany Fiber TREVIRA Trevira GmbH, Bi-ComponentCore/sheath PES/ Staple Fiber 255 Germany Fiber Polyethylene VESTAMELTEvonik Industries AG, Co-Polyester Co-Polyester Powder 4680-P1 Germanypowder AERODISP Evonik Industries AG, Nanoparticle Al₂O₃ 30% W 630Germany dispersion in water VP Dispersion Evonik Industries AG,Nanoparticle ZrO₂ 50% W 2650X Germany dispersion in water AEROSIL 200Evonik Industries AG, Nanoparticle Pyrogenic silica Powder Germany(SiO₂) LAPONITE Southern Clay Products Nanoparticle Layer silicate,Powder or RD Inc., Gonzales/TX, 55% SiO_(2,,) 26% dispersion U.S.A Mg0,6% NaO, 4% P₂O₅ BINDZIL Eka Chemicals AB, Nanoparticle Silica sol (SiO₂)Dispersion CAT 220 Bohus, Sweden

Test Methods Cyclical Compression Test

The test apparatus for the Cyclical Compression Test comprised thefollowing elements:

-   -   a.) A tensile tester model Zwick/Roell Model Z010, obtained from        Zwick GmbH & CoKG, Ulm, Germany, comprising a lower fixed        portion with a load cell capable of measuring forces up to 10 kN        and an upper portion movable apart from the lower portion in the        vertical direction at a rate defined as the “crosshead speed”;    -   b.) A test fixture consisting of 2 stainless steel blocks with a        base area of 6 cm×8 cm each containing heating elements capable        of heating the blocks independently of each other to at least        900° C. The lower stainless steel block is firmly attached to        the load cell and the upper steel block is firmly attached to        the upper movable portion (crosshead) of the tensile tester so        that the base areas of the blocks are positioned vertically        above each other. Each stainless steel block is equipped with a        thermal couple, which is located in the center of the block;    -   c.) A laser extensiometer obtained from Fiedler Optoelektronik,        Lützen, Germany, which measures the open distance between the        stainless steel blocks.

Mounting mat samples to be tested had a diameter of approximately 2inches (51 mm) and were positioned directly on the lower stainless steelblock.

The gap was then closed compressing the mounting mat to a definedcompressed density, also referred to as open gap. The pressure exertedby the mounting mat was recorded after one minute relaxation in the opengap position. After this both stainless steel blocks were heated with arate of 30° C. per minute until the defined test temperature wasreached. During this time the gap between the stainless steel blocks waskept constant (i.e., the metal expansion was continuously compensatedvia the laser extensiometer). The lowest pressure during the heat-upperiod was recorded.

After heat-up the cycling started by closing the gap to a second definedmat density, also referred to as closed gap. Then gap was opened againto the open gap position. This cycle was repeated 500 times. Thecrosshead speed during cycling was 2.5 meters per minute. The open andclosed gap pressures of the last cycle were recorded.

Real Condition Fixture Test (RCFT)

The test apparatus for the RCFT comprised the following:

-   -   a.) A commercially available tensile tester (obtained under the        trade designation “MTS” Model Alliance RT/5, from Material Test        Systems, Eden Prairie, Minn.) comprising a lower fixed portion        and an upper portion movable apart from the lower portion in the        vertical direction at a rate defined as the “crosshead speed”        and bearing a load cell capable of measuring forces up to 5 kN;    -   b.) A test fixture consisting of 2 stainless steel blocks with a        base area of 6 cm×8 cm each containing heating elements capable        of heating the blocks independently of each other to at least        900° C. The lower stainless steel block is firmly attached to        the lower fixed portion and the upper steel block is firmly        attached to the load cell at the upper movable portion        (crosshead) of the tensile tester so that the base areas of the        blocks are positioned vertically above each other. Each        stainless steel block is equipped with a thermal couple, located        in the centre of the block;    -   c.) A laser extensiometer obtained from Fiedler Optoelektronik,        Lützen, Germany, which measures the open distance (gap) between        the stainless steel blocks.    -   A mounting mat sample having dimensions of 44.5 mm×44.5 mm was        placed between the stainless steel blocks. The gap was closed        with a crosshead speed of 1.0 m/min to a defined mounting mat        density. After this each stainless steel block was heated        incrementally to a different temperature profile to simulate the        temperature of the metal housing and the ceramic substrate in an        exhaust gas treatment device. During heating, the gap between        the stainless steel blocks was increased by a value calculated        from the temperatures and thermal expansion coefficients of a        typical exhaust gas treatment device housing and ceramic        substrate.    -   The RCFT's were carried out with two different temperature        profiles here. The first profile simulates a maximum temperature        of the ceramic substrate of 500° C. and a maximum temperature of        the metal can of 200° C. The second profile simulates maximum        temperatures of 700° C. for the ceramic substrate and 400° C.        for the metal can.    -   After heating to the maximum temperature, the stainless steel        blocks were cooled incrementally and the gap was decreased by a        value calculated from the temperatures and thermal expansion        coefficients. The pressure exerted by the mounting mat during        the heating and cooling cycle was recorded. The mounting mat        sample and the steel blocks were cooled to 35° C. and the cycle        was repeated two more times while the pressure exerted by the        mounting mat was recorded. A minimum pressure of at least 50 kPa        for each of the 3 cycles is typically considered desirable for        mounting mats.

Examples 1A, 1B and C1

In Comparative Example C1, an intumescent mounting mat of the followingcomposition was prepared:

Composition of Comparative Example C1 (Parts Per Weight)

46.2% fiber (““SUPERWOOL” 607HT”)

11.5% chopped R-glass fiber 6 mm long, heat treated for 1 hour at 700°C.

38.5% unexpanded vermiculite

3.8%—P1 powder (“VESTAMELT 4680”)

The intumescent mounting mat of comparative example C1 was made on a 310mm wide non-woven-machine built, obtained from Formfiber, Denmark, andoperating according to the method disclosed above. The forming box ofthis machine essentially corresponded to the schematic drawing shown inFIG. 2 whereby the forming box had two rows of three spike rollsarranged opposite each other in the upper part and two rows of threespike rolls arranged opposite each other near the bottom of the formingbox. An endless belt screen ran between these upper and lower spike rowsas shown in FIG. 2. A forming wire was arranged below the bottom of theforming box.

The inorganic fibers and the polymeric powder were fed into the machinevia a transportation belt. At first the fibers were passed through apre-opening section with 2 rotating spike rolls. After this the fiberswere blown into the top of the forming chamber. The vermiculite was thenfed directly into the top of the forming section via a secondtransportation belt. The fibers and particles were collected on theforming belt, which was moving at a speed of about 1 m/min. A thin papernon-woven scrim with an area weight of about 18 g/m² was fed into thelower part of the forming chamber in order to support the mat duringtransportation. After the forming section the mat was passed though ahot air oven. The oven temperature was at 140° C., which heat activatedthe polymeric powder. Directly after the oven the mat was compressedwith a roller in such a way that the originally formed thickness ofabout 25 mm was reduced to about 8 mm.

These mounting mats (examples) were then subjected to cyclic compressiontesting and the Real Condition Fixture Test (RCFT).

Example 1A

The intumescent mounting mat of Example 1A was prepared in the samemanner as described above with the exception that 1.0% (related to totalmat composition) of dispersion (obtained under the trade designation“AERODISP W 630” from Evonik Industries AG, Frankfurt, Germany) wasevenly sprayed onto the fibers on the transportation belt using a manualpump sprayer, before they were fed into the pre-opening section.

Example 1B

The intumescent mounting mat of Example 1B was prepared in the samemanner as described above with the exception that 3.0% (related to thetotal mat composition) of dispersion (obtained under the tradedesignation “VP DISPERSION W2650X” from Evonik Industries AG, Frankfurt,Germany) was evenly sprayed onto the fibers on the transportation beltusing a manual pump sprayer, before they were fed into the pre-openingsection.

TABLE 1 Cyclic Compression Test @ 500° C., mount densities 0.73 g/cm³(open gap) and 0.80 g/cm³ (closed gap) Starting pressure - LowestPressure Pressure after 500 1 minute during Heat-up Cycles - open gapExample No. relaxed (kPa) (kPa) (kPa) C1 285 144 48 1A 458 192 51 1B 514209 55

TABLE 2 Results from RCFT at mount density 0.8 g/cm³ Simulation ofmaximum 500° C. monolith surface temperature and maximum 200° C. cantemperature Example Starting Pressure Lowest Pressure in Lowest Pressurein No. (kPa) Cycle 1 Cycle 3 C1 402 160 145 1A 651 193 167 1B 723 192164

The results from Cyclic Compression Test and RCFT illustrate theimprovement of the holding pressure performance for both intumescent matexamples containing nanoparticles (“AERODISP W 630” and “VP DISPERSIONW2650X”) versus the Comparative Example C1.

Examples 2A, 2B and C2 Comparative Example C2

In Comparative Example C2, a mounting mat having the followingcomposition was made:

Composition of Comparative Example C2

32.4% fibers (“SUPERWOOL 607HT”)

32.4% chopped R-glass fiber 36 mm long, heat treated for 1 hour at 700°C.

32.4% chopped (“BELDOTEX 225”) 6 mm long, heat treated for 1 hour at800° C.

2.9% Bi-component fibers (“TREVIRA 255”)

The mounting mat of Comparative Example C2 was made on a 310 mm widenon-woven-machine built as described above in Comparative Example C1.

The inorganic fibers and the binder fibers were fed into the machine viaa transportation belt. At first the fibers were passed through apre-opening section with 2 rotating spike rolls. After this the fiberswere blown into the top of the forming chamber. The fibers were thencollected on the forming belt moving at a speed of about 1 m/min. A thinpaper non-woven scrim with an area weight of about 18 g/m² was fed intothe lower part of the forming chamber in order to support the mat duringtransportation. After the forming section the mat was passed though ahot air oven. The oven temperature was at 140° C. for heat activatingthe binder fibers. Directly after the oven the mat was compressed with aroller in such a way that the originally formed thickness of about 45 mmwas reduced to about 13 mm.

Composition of Example 2A

The mounting mat of Example 2A was prepared in the same manner asdescribed above for Comparative Example C2 with the exception that 10%nanoparticle dispersion (related to the total mat composition) (obtainedunder the trade designation “BINDZIL CAT 220” from Eka Chemicals,Sweden), which was diluted to 5% solids, was evenly sprayed onto thefibers on the transportation belt using a manual pump sprayer, beforethey were fed into the pre-opening section.

Composition of Example 2B

The mounting mat of Example 2B was prepared in the same manner asdescribed above for Comparative Example C2 with the exception that 2.8%(related to the total mat composition) of nanoparticles (obtained underthe trade designation “AEROSIL 200” from Evonik Industries, Germany)were manually added onto the fibers on the transportation belt beforethey were fed into the pre-opening section.

TABLE 3 Cyclic Compression Test @ 500° C.; mount densities 0.50 g/cm³(open gap) and 0.55 g/cm³ (closed gap) Lowest Starting Pressure Pressureafter pressure - during Pressure after 500 Cycles - Example 1 minuteHeat-up 500 Cycles - closed gap No. relaxed (kPa) (kPa) open gap (kPa)(kPa) C2 252 47 18 212 2A 447 126 43 309 2B 354 166 55 310

The Cyclic Compression Test results show a good pressure increase forboth examples using nanoparticles (“BINDZIL CAT 220” and “AEROSIL 200”).

TABLE 4 Results from RCFT, mount density 0.5 g/cm³ Simulation of maximum500° C. monolith surface temperature Simulation of maximum 700° C. andmaximum 200° C. monolith surface temperature and can temperature maximum400° C. can temperature Starting Lowest Lowest Starting Lowest LowestExample Pressure Pressure in Pressure in Pressure Pressure in Pressurein No. (kPa) Cycle 1 Cycle 3 (kPa) Cycle 1 Cycle 3 C2 285 54 54 275 2725 2A 493 131 126 480 81 67 2B 371 153 138 414 88 77

The RCFT results show a good pressure increase for both examples usingnanoparticles in both RCFT tests. Specifically the improvements of thelowest pressures under simulated use conditions in cycle 1 and 3 areremarkable (>100%).

Examples C3 and 3A

Comparative Example C3 and Example 3A having the compositions describedbelow were produced according to the process described above for themaking of the mounting mats of Examples C2, 2A and 2B. In addition tothe heat bonding process of the binder fibers after the forming section,the mat was needled with 24 punches per cm² using a needle tacker(obtained from Dilo, Eberbach. Germany).

Composition of Comparative Example C3

31.8% fibers (“ISOFRAX”)

31.8% fibers (“SAFFIL 3D+”)

31.8% chopped silica fibers 65 mm long (obtained under the tradedesignation “SILICA YARN K11C” from Steklovolokno); the fibers were heattreated in a kiln at 800° C. for 1 hour

4.6% Bi-component fibers (“TREVIRA 255”)

Composition of Example 3A

A sample with the same composition as the mounting mat of ComparativeExample 3 was impregnated with a 0.5% suspension of nanoparticles(“LAPONITE RD”) in water, by immersion of the mat in the suspension andsubsequent drying in an oven at 120° C. for 50 min.

TABLE 5 Cyclic Compression Test @ 500° C.; mount densities 0.52 g/cm³(open gap) and 0.58 g/cm³ (closed gap) Lowest Pressure Pressure after500 Pressure after 500 Example during Cycles 500 - open Cycles 500 -closed No. Heat-up (kPa) gap (kPa) gap (kPa) C3 42 16 182 3A 198 46 390

A significant (>100%) pressure increase of the nanoparticles (“LAPONITERD”) containing mounting mat versus the Comparative Example C3 withoutnanoparticle incorporation can be seen.

Foreseeable modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes.

What is claimed is:
 1. A method of making a mounting mat comprising thesteps of: (i) supplying inorganic fibers through an inlet of a formingbox having an open bottom positioned over a forming wire to form anon-woven mat of fibers on the forming wire, the forming box having aplurality of fiber separating rollers provided in at least one row inthe housing between the inlet and housing bottom for breaking apartclumps of fibers and an endless belt screen; (ii) capturing clumps offibers on a lower run of the endless belt beneath fiber separatingrollers and above the forming wire; (iii) conveying captured clumps offibers on the endless belt above fiber separating rollers to enablecaptured clumps to release from the belt and to contact and be brokenapart by the rollers; (iv) transporting the non-woven mat of fibers outof the forming box by the forming wire; and (v) compressing thenon-woven mat of fibers and restraining the non-woven mat of fibers inits compressed state thereby obtaining a mounting mat having a desiredthickness suitable for mounting a pollution control element in thehousing of a pollution control device; wherein inorganic particleshaving an average diameter of 1 nm to 100 nm are provided in themounting mat.
 2. The method according to claim 1, wherein the inorganicparticles are provided in the mounting mat by supplying a powder ofinorganic particles to the forming box.
 3. The method according to claim1, wherein the inorganic particles are provided in the mounting mat byspraying a dispersion of the inorganic particles on the inorganic fibersbefore supplying the inorganic fibers to the forming box or by sprayingthe dispersion on the non-woven mat of fibers before or aftercompression thereof.
 4. The method according to claim 1, wherein themounting mat is free of organic binder or contains organic binder in anamount of not more than 5% by weight, based on the total weight of themounting mat.
 5. The method according to claim 1, wherein the inorganicparticles are provided in the mounting mat in an amount in the range offrom at least 0.5% to 10% by weight.
 6. The method according to claim 1,further comprising: providing intumescent material in the mounting mat.7. The method according to claim 1, wherein the supplied inorganicfibers are selected from melt formed ceramic fibers including annealedmelt-formed ceramic fibers, sol-gel formed ceramic fibers,polycrystalline fibers, glass fibers including heat treated glassfibers, alumina-silica fibers, biosoluble fibers, and combinationsthereof.
 8. The method according to claim 1, further comprising:needle-punching or stitch-bonding the mounting mat
 9. The methodaccording to claim 1, wherein the mounting mat further comprises one ormore layers selected from scrims and nettings.
 10. The method accordingto claim 1, further comprising: disposing a scrim or netting on one orboth opposite major sides of the mounting mat.
 11. The method accordingto claim 9, wherein the scrim or netting comprises inorganic fibers. 12.The method according to claim 1, wherein the inorganic particlescomprise oxides of silica, alumina or zirconia, titania or silicates.13. The method according to claim 1, wherein the inorganic particles areevenly distributed within the non-woven mat.
 14. The method according toclaim 6, wherein the intumescent material is evenly distributed withinthe non-woven mat.
 15. The method according to claim 6, wherein themounting mat is an intumescent mounting mat.
 16. The method according toclaim 9, further comprising: providing intumescent material in themounting mat.
 17. The method according to claim 1, wherein the non-wovenmat contains more of the inorganic fibers by weight than the inorganicparticles.
 18. A method of making a pollution control device comprisingthe steps of: providing a housing, a pollution control element, and amounting mat; disposing the pollution control element within thehousing; and disposing the mounting mat between the pollution controlelement and the housing so as to maintain the position of the pollutioncontrol element within the housing and for absorbing mechanical andthermal shock, wherein the mounting mat is made according to the methodof claim
 1. 19. The method of claim 17, wherein the inorganic particlesare evenly distributed within the non-woven mat.
 20. The method of claim17, wherein the mounting mat is an intumescent mounting mat.